Imaging Radar / Non-Imaging Radar

An Imaging Radar forms a picture of the observed object or area.
Imaging radars have been used to map the Earth, other planets, asteroids, other celestial objects
and to categorize targets for military systems.

Typically implementations of a Non-Imaging Radar system are speed gauges and radar altimeters.
These are also called scatterometers since they measure the scattering properties of the object
or region being observed. Non-Imaging Secondary Radar applications are immobilizer systems in some
recent private cars.

Primary Radar

A Primary Radar
transmits high-frequency signals which are reflected at targets.
The arisen echoes are received and evaluated. This means, unlike
secondary radar sets
a primary radar set receive it's own emitted signals as an echo again.

Secondary Radar

At these radar sets the airplane must have a
transponder (transmitting responder)
on board and this transponder responds to interrogation by transmitting a coded reply signal. This response
can contain much more information, than a primary radar set is able to acquire (E.g. an
altitude,
an identification code or also any technical problems on board such as a radiocontact loss ...).

Pulsed Radars

Pulse radar sets
transmit a high-frequency impulse signal of high power.
After this impulse signal, a longer break follows in which the echoes can be received,
before a new transmitted signal is sent out.
Direction,
distance and sometimes if necessary the
height or
altitude
of the target can be determined from the measured antenna position and propagation time of the pulse-signal.

Continuous- Wave Radar

CW radar sets transmit a high-frequency signal continuously.
The echo signal is received and processed. The receiver need not to be mounted at the same place
as the transmitter. Every firm civil radio transmitter can work as a radar transmitter at
the same time, if a remote receiver compares the propagation times of the direct signal with
the reflected one. Tests are known that the correct location of an airplane can be calculated
from the evaluation of the signals by three different television stations.

Unmodulated CW- Radar

The transmitted signal of these equipments is constant in amplitude and frequency.
These equipment is specialized in speed measurings. Distances cannot be measured.
E.g. they are used as
speed gauges
for police. Newest equipments
(LIDAR)
work in the laser frequency range and measure not only the speed.

Modulated CW- Radar

The transmitted signal is constant in the amplitude but
modulated in the frequency.
This one gets possible after the principle of the
propagation time measurement
with that again.
It is an advantage of this equipment that an evaluation is carried out without
reception break and the measurement result is therefore continuously available.
These radar sets are used where the measuring distance isn't too large and it's necessary
a continuous measuring (e.g. an altitude measuring in airplanes or as weather radar/windprofiler).

A similar principle is also used by radar sets whose transmitting impulse is too long to get
a well distance resolution. Often this equipment modulate its transmitting pulse to obtain
a distance resolution within the transmitting pulse with the help of the
pulse compression.

Bistatic Radar Sets

A bistatic radar consists of a separated
(by a considerable distance) transmitting and receiving sites.